Tarjan's Algorithm

//Tarjan's Algorithm


import java.util.*;
public class TarjanSCC
{
  
  static HashMap<Integer,List<Integer>> adj=new HashMap<>();
  static int Disc[]=new int[8];
  static int Low[]=new int[8];
  static boolean inStack[]=new boolean[8];
  static Stack<Integer> stack=new Stack<>();
  static int time = 0;
  
  static void DFS(int u)
  {
Disc[u] = time;
Low[u] = time;
time++;
stack.push(u);
inStack[u] = true;
    List<Integer> temp=adj.get(u); // get the list of edges from the node.
    
    if(temp==null)
    return;
    
for(int v: temp)
{
if(Disc[v]==-1) //If v is not visited
{
DFS(v);
Low[u] = Math.min(Low[u],Low[v]);
}
//Differentiate back-edge and cross-edge
else if(inStack[v]) //Back-edge case
Low[u] = Math.min(Low[u],Disc[v]);
}
 
if(Low[u]==Disc[u]) //If u is head node of SCC
{
System.out.print("SCC is: ");
while(stack.peek()!=u)
{
System.out.print(stack.peek()+" ");
inStack[stack.peek()] = false;
stack.pop();
}
System.out.println(stack.peek());
inStack[stack.peek()] = false;
stack.pop();
}
  }
 
static void findSCCs_Tarjan(int n)
  {
    for(int i=1;i<=n;i++)
    {
        Disc[i]=-1;
        Low[i]=-1;
        inStack[i]=false;
    }
 
for(int i=1;i<=n;++i)
{
if(Disc[i]==-1)
DFS(i);   // call DFS for each undiscovered node.
}
  }
 
  public static void main(String args[])
  {
    adj.put(1,new ArrayList<Integer>());
    adj.get(1).add(3);
    
    adj.put(2,new ArrayList<Integer>());
    adj.get(2).add(1);
adj.put(3,new ArrayList<Integer>());
adj.get(3).add(2);
adj.get(3).add(4);
 
adj.put(4,new ArrayList<Integer>());
adj.get(4).add(5);
adj.put(5,new ArrayList<Integer>());
adj.get(5).add(6);
adj.put(6,new ArrayList<Integer>());
adj.get(6).add(7);
adj.put(7,new ArrayList<Integer>());
adj.get(7).add(4);
 
findSCCs_Tarjan(7);
  }
 
}